Synthesis Of L-Menthyl Acetic by Esterification L-Menthol and Acetic Anhydride with Variation Of Time

l-menthyl acetic is an ester with specific aroma that synthesized by reaction of l-menthol and acetic anhydride and useful in fragrance industry. This paper reports influenced variation of time reaction toward ester product and characteristics l- menthyl acetic based on TLC, FTIR, GC and GC-MS. Reaction using l-menthol, acetic anhydride and catalyst H­2­SO­4­ 98 % in diethyl eter solvent at temperature 60 °C with variation of time reaction (45, 60, 75, 90, 105 minutes). The result of research is variation of time influence product with highest yield 88,43 % for 90 minutes. Monitoring TLC achived R­f­ = 0,82; analysis by FTIR achived specific wave number ester 1736,96 cm-1; analysis by GC achived t­r­ = 14,82 minutes and analysis by GC-MS achived t­r­ = 16,13 minutes with base peak m/z = 95.


INTRODUCTION
Menthol is a major component in peppermint oil that can be produced from the distillation of leaves Mentha x pipertits (Raharjo, 2013), with a distinctive aroma of peppermint and give effect to the taste. l-menthol compounds included monocyclic monoterpenes class (Moon, 2004) with the chemical formula C 10 H 20 O (Stolle and Hopf, 2009). Conversation l-menthol to ester can be form by reaction using acetic anhydride by esterification with sulfate acid as catalyst (Sastrohamidjojo, 2004). This reaction known as esterification Fischer (Carey, 2000). Chasana research (2014), gained influence ratio mole from l-menthol: acetic anhydride (2:1) with the highest yield l-methyl acetic 28,28 % at temperature 60 °C for 60 minutes, but have not obtained information influence variation of time between lmenthol and acetic anhydride in esterification reaction to yield l-methyl acetic. So, in this study will reaction with variation of time for 45, 60, 75, 90, 105 minutes (Hikmah dan Zuliyana, 2010).
Variation of time provide information the influence the variation of time to yield of an ester to be obtained. Theoretically, increasing reaction time at Fischer esterification can increase the amount of product formed, this is caused by the increase in the intensity of collision between the reactants in the form of products (Fatmawati and Shakti, 2013).

Monitoring Synthesis Mixture by TLC
Activation of the TLC plate silica GF 254 use the oven for 20 minutes at 100 ° C. The next l-menthol and l-methyl acetic spotted at a distance of 1,0 cm from the bottom edge of the TLC plate and eluted using a capillary tube to a distance of 8.5 cm. Eluent used is n-hexane and ethyl acetate in a ratio of 9:1 Then the plate is dried and sprayed with a solution of 5 % H 2 SO 4 in methanol. After the plates dry and then heated on a hotplate to show two pieces of brownish yellow stains on the plate. R f its calculated value and compared with R f l-menthol 0,40 (Pelter, et al., 2008) and l-methyl acetic suspected to have R f 0,80 to 0,83 .

Separation Synthesis Mixed Result
The results of the synthesis mixture is put into separating funnel 250 mL. pH synthesized checked using universal pH paper. NaHCO 3 5 % added in solution until pH up to pH distilled water (pH = 5). Then the mixture was shaken and allowed for 5 minutes until the organic phase and aqueous phase separate apparent. Organic phase containing a mixture of compounds comprising ester compound l-methyl acetic, lmenthol and solvent diethyl ether while the water phase is composed of neutral salts. The organic phase is collected in glass beaker 250 mL and added Mg2SO 4 anhydrous. Furthermore, the organic phase is separated from MgSO 4 anhydrous by decanted carefully and slowly then accommodated in the tube vial. Nitrogen gas Suryani, et.al.

Synthesis of L-Methyl Acetic by Esterification L-Menthol and Acetic Anhydride with Variation of Time
Al-Kimia | Volume 8 Nomor 1 2020 67 flowed on the surface and the bottom of the tube vial, weighed to constant weight.
Having obtained a constant weight, closed tube vial using aluminum foil wrapped up tightly and stored in freezer.

Characterization of Physical Properties Mixed Result Synthesis
Characteristic of physical properties of the mixture of compounds synthesized (aroma and color). Determination of density performed by weighing as much as 2 mL of compounds synthesized using 2 mL pycnometer. Measured temperature of mixture synthesis result using a thermometer. The density value is calculated using the formula: The formula consists of p as density at T (°C), ρ' as density at T'(°C), k is correction factor and T is temperature mixture synthesis Determination refractive index of compound synthesized were determined by Atago Hand Refractometer. Before the measurement are made, cleaned first the tool refractometer with 95% ethanol and then calibrated using distilled water. Subsequently, the sample was dropped on the prism 2 drops. The reading of the refractive index of samples was made during light-dark boundary of the line right at the intersection of the prism. Refractive index values calculated by the formula: The formula consists of n as refractive index at T (°C), n' as refractive index at T'(°C), k as correction factor and T as temperature mixture synthesis Characterization by FTIR l-menthol, acetic anhydride, and l-methyl acetic dropped into the scouring KBr pellet. Furthermore KBr pellet is placed in the cell holder through which the light beam and made its IR spectrum at wave number range 4000 -400 cm -1 .

Characterization by GC
A total of 0.01 mL of l-menthol and l-methyl acetic injected into the inlet using syiringe GC HP 5890 instrument with temperature column and detector 250°C, gas flow rate of 2 mL/min, FID detector. The data obtained in the form of a chromatogram. % Peak area is used to determine the ratio of constituent compounds synthesized by the following equation 3.
While the mass of l-methyl acetic research result obtained using the equation 4.

Characterization by GC-MS
A total of 0,01 mL of l-menthol and l-methyl acetic using syringe injected into the GC-MS instrument inlet Aglient 6980N Network GC System with detector temperature at 300 °C , gas flow rate of 1,3 mL/min, detector Aglient 5973 inert MSD, Data from instrument such as mass spectra GC-MS, further interpretation of spectral data and comparing the mass spectra of l-menthol and l-methyl acetic with the standards of library Willey version 7.0.

RESULT AND DISCUSSION
Results obtained by esterification of the compound in the form of a yellow liquid and a distinctive smell of mint with the results of the monitoring TLC chromatogram obtained in the form of two brownish yellow stains with a stain I R f = 0,41; while R f stain II = 0,82 allegedly was R f product. Characterization of physical properties obtained density of 1,1055 g/ml and the refractive index of 1,4426. Characterization of the results of the synthesis mixture is done by FTI, GC, and GC-MS. IR spectral data indicate that the ester group C = O stretching vibration at wavenumber 1736,96 cm -1 , C-O stretching vibration at wavenumber 1245,82 cm -1 . Besides the OH stretching vibration at wave number 3454,03 cm -1 and C-O stretching vibration of secondary alcohols at wave number 1023,32 cm -1 shows that the results of the synthesis mixture still contains l-menthol. Analysis by GC shows have been formed compound l-methyl acetic. Analysis of the result of the synthesis mixture with chromatogram obtained GC 2 peaks, peak I with t r = 11,71 minutes allegedly is l-menthol while peak II with t r = 14,82 minutes is suspected l-methyl acetic, the compound had t r longer than l-menthol is because it is nonpolar making it retained on the column . The following analysis of the data presented by GC against the constituent compounds synthesized as in Table 1.

Tabel 1. Yield (%) of l-methyl acetic
Based the yield results in Table 1, show that the highest yield was obtained at reaction time 90 minutes which is 88.43%. This shows that with increasing reaction time given will increase the yield of the synthesis product, but with a decrease in the yield explain that if a reactant which have reacted has reached the optimum time to collide then Suryani, et.al.

Synthesis of L-Methyl Acetic by Esterification L-Menthol and Acetic Anhydride with Variation of Time
Al-Kimia | Volume 8 Nomor 1 2020 69 the extension reaction time will not yield more (Ozgul and Turkey, 2002in : Widyawati, 2007in Kasim, 2012. Then, the highest yield results is analyzed using GC-MS. GC-MS analysis of the obtained two peaks, peak I with t r = 13.30 minutes suspected l-menthol produce fragment ion peak at m/z = 29,41,55,71,81,95,109,123,138,147,155,191,207,281. The secondary alcohol, the peak was observed due to release of H atom shown in Figure  2.
While the base peak obtained m/z = 95 shown in Figure 5. Besides the release of atom O at position α is shown in Figure 6 with m/z = 43 obtained result that are spesific termination ester.

CONCLUSION
Variation of time influence yield of l-methyl acetic 88,43% with optimum time is 90 minutes and characterization of the product l-methyl acetic by monitoring TLC result obtained R f which was0,41 is l-menthol and R f which was 0,82 is l-methyl acetic. FTIR results with typical absorption of functional groups C = O and C-O ester at wave number 1736,96 cm -1 and 1245,82 cm-1 . Results chromatogram GC with a value t r which was 14,82 minutes is l-methyl acetic. GC-MS results with t r which was 16,13 minutes is l-methyl acetic.